Lesson 33: Osmolality and USG

What analytical test assesses urine solute concentration by refractormetry?

USG

What is the adequate concentration of urine in a dog that is dehydrated?

>1.030

What is the inadequate concentration of urine in a dog that is dehydrated?

<1.030

If a dehydrated dog has a USG that is less than 1.030 what would we be worried about?

The kidneys ability to concentrate the urine

What is the adequate concentration of urine in a cat that is dehydrated?

>1.040

What is the inadequate concentration of urine in a cat that is dehydrated?

<1.040

What is the adequate concentration of urine in a large animal that is dehydrated?

>1.025

What is the inadequate concentration of urine in a large aminal that is dehydrated?

<1.025

How do you estimate the osmolality of urine from the USG?

Multiply the last two digits of USG by 30

What are the exceptions when calculating urine osmolality to USG?

Protein and glucose

What do you subtract from the USG for every 1g/dL of protein or glucose?

0.005

Why is it important to subtract the proteins and glucose from the USG?

USG overestimates the solute concentration if there is increased protein or glucose concentrations

What is the function of the Glomerular filtration?

Substances filter from plasma to tubules, excluding proteins such as albumin

What is the major process of the proximal tubule?

to reabsorb electrolytes, HCO3-, Ca, Mg, Urea, Glucose, AA

What is absorbed in the thin descending segment of the loop of Henle?

Water

What is reabsorbed in the thick ascending loop of Henle?

Na Cl K

What is reabsorbed in the Distal tubule?

Na Cl

What is reabsorbed in the collecting tubule?

Aldosterone mediated 3 Na+ 1Cl resorption, Ureas.

What is secreted in the collecting tubule?

K

In which parts of the nephron is water reabsorbed?

PCT, Descending LOH, DCT, CT via ADH

What tubular segment resorbs water under the influence of ADH?

Collecting duct

Describe the osmolality of the proximal tubule?

removes both volume and solutes causing no change in concentration

Describe the osmolality of Descending LOH?

Removes H20, concentrating the urine

Describe the osmolality of the Ascending LOH?

Removes solutes, diluting the urine

Describe osmolality of the collecting duct?

removes the rest of the H20, concentrating the urine and increasing the osmolality

What are the three things that are needed to produce concentrated urine?

ADH

Tubules must respond to ADH

Concentration gradient

What portion of the nephron reabsorbs water and electrolytes resulting in osmolality same as plasma?

Proximal tubules

For kidneys to produce urine with the SG of 1.001-1.003 or osmolality of 100mmol/kg, what nephron segment must be functional?

Ascending loop of Henle

For kidneys to produce a urine with a specific gravity of 1.030 (osmolality of 1500 mmol/kg), which portion of the nephron must be functional?

CT, ALOH, DLOH, PCT

What is a very concentrated urine called?

Hypersthenuria

What is considered a very high urine concentration in dogs?

>1.050

What is a very high urine concentration in a cat?

>1.060

What is a normal concentrated urine called?

Euthenuria

What is considered the normal urine RI for a dog?

1.015-1.045

What is considered the normal urine RI for a cat?

1.035-1.060

What is urine concentration called that is the same as the plasma osmolality?

Isosthenuria

What is considered the isosthenuria urine RI?

1.007-1.013 or when Urine osmolality= 300

What is a very low urine concentration called?

Hyposthenuria

What is considered the Hyposthenuria urine RI?

USG <1.007

If you have a high USG what does that say about the volume of urine?

Low urine volume

If you have a low USG, what does that say about the volume of urine?

High urine volume

What knowledge must you have to interpret the USG?

Hydration status

What is azotemia?

Increase metabolic waste in the blood

What is polyuria?

High volume of urine

What is oliguria or anuria?

Low to no urine volume

What does Hydration status measure?

Total body water

What is blood volume based on?

Water

What is Plasma osmolality based on?

Solutes such as NaCl

What is ADH release based on?

Stimulus of ADH

What does the factor tubular response mean?

Collecting ducts ability to respond to ADH

What does the concentration gradient measure?

That the medullary interstitial gradient is preserved

What does the water conservation mean?

The kidneys ability to conserve water

A cat presents with USG of 1.065, what condition is most likely causing the USG result?

Dehydration

A cat presented with mild dehydration. The cat was treated at a vet clinic with IV fluids. Following treatment, USG was 1.002. What condition is most likely causing the USG result?

Overhydration

A cat presents with dehydration and glucoscuria of 4+ ad USG of 1.025. What condition is most likely causing the USG result?

Osmotic or solute diuresis

A cat presents with severe dehydration and anorexia for three months with oliguria. USG is 1.011. What condition is most likely causing the USG result?

Damage to nephrons

An intact female dog presents with fever, inflammatory, leukogram, and high urine volume with USG of 1.003. What condition is most likely causing the USG.

Collecting tubule not responding to ADH